Distal bone anchors for bone fixation with secondary compression

ABSTRACT

Disclosed is a bone fracture fixation device, such as for reducing and compressing fractures in the proximal femur. The fixation device includes an elongate body with a helical cancellous bone anchor on a distal end. An axially moveable proximal anchor is carried by the proximal end of the fixation device. The device is rotated into position across the fracture or separation between adjacent bones and into the adjacent bone or bone fragment, and the proximal anchor is distally advanced to apply secondary compression and lock the device into place. The device may also be used for soft tissue attachments.

PRIORITY INFORMATION

This invention is a continuation-in-part of U.S. patent application Ser.No. 09/822,803, filed Mar. 30, 2001 now U.S. Pat. No. 6,511,481, theentire contents of which are hereby expressly incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to internal bone fracture fixationdevices. In one application, the present invention relates to bonefracture fixation devices and methods adapted for fixation, among otherfractures, of femoral neck and other proximal femoral fractures.

2. Description of the Related Art

The femur, otherwise known as the thigh bone, generally comprises anelongate shaft extending from the hip to the knee. The proximal end ofthe shaft includes a head, a neck, a greater trochanter and a lessertrochanter. The head of the femur fits into the acetabular cup of thehip bone to form a ball and socket joint at the hip. The distal end ofthe femur includes a medial condyle and a lateral condyle. The condylesengage an upper end of the tibia to form the knee joint. Overall, thefemur is the longest and strongest bone in the skeleton. However,portions of the femur are extremely susceptible to fracturing.

Pertrochanteric fractures among geriatric patients are the most frequentin connection with those of the region of the neck of the bone. Theadvanced age and the pathologies which are encountered in these patientsmake a timely stabilization of skeletal injuries necessary in order toreduce to a minimum the bed confinement and the rehabilitation times.Preferably, devices and procedures are utilized which minimizecomplications brought about by the so-called immobilization syndrome,which may be lethal for patients in delicate metabolical circumstances.It is also preferable to reduce to a minimum blood losses related tosurgical intervention. At the same time, the syntheses means utilizedmust be stable in order to allow the patient to very timely assume aseated position and, two or three days following the intervention, toreassume an erect posture with progressive bearing of weight.

Internal fixation of femoral fractures in general is one of the mostcommon orthopedic surgical procedures. Fractures of the femur occur inboth the proximal portion of the femur and the distal portion of thefemur. Fractures of the proximal portion of the femur (hip fractures)are generally classified as femoral neck fractures (capital orsub-capital), intertrochanteric fractures and subtrochanteric fractures.Fractures of the distal portion of the femur (knee fractures) arereferred to as supracondylar fractures. Supracondylar fracturesgenerally extend vertically between the condyles at the lower end of thefemur to separate the distal portion of the femur into two main bonefragments. A fracture line may be further comminuted to create aplurality of smaller bone fragments. Fractures of the femur which extendinto the neck of the bone are generally more difficult to treat thanfractures restricted to the shaft of the femur.

Operative treatment of the fractures requires that the fractures beinternally fixed and possibly compressed. Fractures of the neck, head ortrochanters of the femur have been treated with a variety of compressionscrew assemblies which include generally a compression plate having abarrel member, a lag screw and a compressing screw. The compressionplate is secured to the exterior of the femur and the barrel member isinserted into a predrilled hole in the direction of the femoral head.The lag screw which has a threaded end and a smooth portion is insertedthrough the barrel member so that it extends across the break and intothe femoral head. The threaded portion engages the femoral head. Thecompressing screw connects the lag screw to the plate. By adjusting thetension of the compressing screw the compression (reduction) of thefracture can be adjusted.

A variety of elongated implants (nail, screw, pin, etc.) have beendeveloped, which are adapted to be positioned along the longitudinalaxis of the femoral neck with a leading (distal) end portion in thefemoral head so as to stabilize a fracture of the femoral neck. Theelongated implant may be implanted by itself or connected to anotherimplant such as a side plate or intramedullary rod. The leading endportion of the implant typically includes means to positively grip thefemoral head bone (external threads, expanding arms, etc.), but theinclusion of such gripping means can introduce several significantproblems. First, implants with sharp edges on the leading end portion,such as the externally threaded implants, exhibit a tendency to migrateproximally towards the hip joint weight bearing surface afterimplantation. This can occur when the proximal cortical bone hasinsufficient integrity to resist distal movement of the screw head. Suchproximal migration under physiological loading, which is also referredto as femoral head cut-out, can lead to significant damage to theadjacent hip joint. Also, the externally threaded implants can generatelarge stress concentrations in the bone during implantation which canlead to stripping of the threads formed in the bone and thus a weakenedgrip. The movable arms of known expanding arm devices are usually freeat one end and attached at the other end to the main body of the leadingend portion of the implant. As a result, all fatigue loading isconcentrated at the attached ends of the arms and undesirably largebending moments are realized at the points of attachment. In addition,conventional threaded implants generally exhibit insufficient holdingpower under tension, such that the threads can be stripped out of thefemoral head either by overtightening during the implantation procedureor during post operative loading by the patient's weight.

Thus, notwithstanding the variety of efforts in the prior art, thereremains a need for an orthopedic fixation device with improved lockingforce such as within the femoral head in a femoral neck application,which resists migration and rotation, and which can be easily andrapidly deployed within the bone.

SUMMARY OF THE INVENTION

There is provided in accordance with one aspect of the presentinvention, a method of securing a first bone fragment to a second bonefragment. The method comprises the steps of drilling a bore through thefirst bone fragment in the direction of the second bone fragment, andadvancing through the bore a fixation device comprising a first portionand a second portion that are coupled to each other. A distal anchor ofthe fixation device is rotated to secure the fixation device to thesecond fragment, and the proximal anchor is axially advanced to engagethe first fragment and provide compression across the fracture.

In one application of the method, the second bone fragment comprises thehead of a femur. Alternatively, the second bone fragment comprises atibia, a fibula, a femur, a humurus, a radius, or an ulna. The firstbone fragment may comprise a condyle.

The method may additionally comprise the step of uncoupling the firstportion from the second portion.

In accordance with another aspect of the present invention, there isprovided a femoral neck fracture fixation device. The device comprisesan elongate body, having a proximal end and a distal end and a helicalanchor on the distal end. The helical anchor is wrapped about a centralcore or axial lumen. An outer edge of the helical anchor defines anouter boundary and the central core or axial lumen defines a minordiameter. A first retention structure is provided on the body, proximalto the anchor. A proximal anchor is moveably carried by the body. Theproximal anchor is movable in the distal direction with respect to thebody and the retention structure resists proximal movement of theproximal anchor with respect to the body.

In accordance with a further aspect of the present invention, there isprovided a bone fracture fixation device. The device comprises anelongate body having a proximal end and a distal end. A cancellous boneanchor is on the distal end. The cancellous bone anchor comprises ahelical flange wrapped about a central core or axial lumen. An outeredge of the helical anchor defines an outer boundary and the centralcore or axial lumen defines a minor diameter. A proximal anchor isaxially movably carried on the body. Complimentary surface structuresare provided between the body and the proximal anchor that permitadvancing the proximal anchor in the distal direction to providecompression across a fracture but that resist axial proximal movement ofthe proximal anchor.

In accordance with another aspect of the present invention, there isprovided a method of treating a femoral fracture. The method comprisesthe steps of drilling at least one and preferably two or three boresdistally into the femur in the direction of a fracture, and advancinginto each bore a fixation device that comprises a body having a firstportion that forms a distal bone anchor and a second portion that formsa proximal end. A proximal component is rotated to engage the distalanchor with the bone distal to the fracture, and a proximal anchor isadvanced distally along the fixation device to compress the fracture.

In accordance with another aspect of the invention a bone fracturefixation device comprises an elongate body having a proximal end and adistal end. The body also includes a helical anchor on the distal end. Afirst retention structure is on the body located proximal to the anchor.A proximal anchor is moveably carried by the body and has a tubularhousing. The tubular housing has at least one barb extending radiallyoutwardly from the tubular housing and defining an engagement surfacethat lies within a plane that is transverse to a longitudinal axis ofthe tubular housing. The proximal anchor is movable in the distaldirection with respect to the body and the retention structure resistsproximal movement of the proximal anchor with respect to the body.

Preferably, the drilling step comprises drilling the bore along an axiswhich extends into the femoral neck and in the direction of the head ofthe femur. In one embodiment, the advancing a proximal anchor stepcomprises axially advancing the proximal anchor without rotating theproximal anchor with respect to the fixation device. The femoralfracture may be a femoral neck fracture (e.g., capital or subcapital),an intertrochanteric fracture or a subtrochanteric fracture.

Further features and advantages of the present invention will becomeapparent to those of skill in the art in view of the detaileddescription of preferred embodiments which follows, when consideredtogether with the attached drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a posterior elevational posterior cross section through theproximal portion of the femur, having two femoral neck fracture fixationdevices positioned therein.

FIG. 2 is a posterior cross section as in FIG. 1, with a modifiedfixation device positioned therein.

FIG. 3A is a side elevational cross section of a fixation device similarto that of FIG. 1.

FIG. 3B is a side elevational cross section of a fixation device similarto that of FIG. 2.

FIG. 3C is a side elevational view of a double helix distal anchor.

FIG. 3D is a side elevational view of a “V” thread distal anchor.

FIG. 3E is a side elevational view of a buttress thread distal anchor

FIG. 3F is a side elevational view of a triple helix distal anchor.

FIG. 3G is a side elevational view of a split triple helix distalanchor.

FIG. 3H is a side elevational view of a tapered transition thread distalanchor.

FIG. 3I is a side elevational view of a tapered thread distal anchor.

FIG. 4A is a front elevational perspective view of a modified fixationdevice of the present invention.

FIG. 4B is a front elevational perspective view of a furthermodification to the fixation device of the present invention.

FIG. 5 is an axial cross sectional view through a distal end of afixation device of the present invention.

FIG. 6 is a posterior cross section as in FIGS. 1, with a fixationdevice and integral proximal plate anchor positioned therein.

FIG. 6A is a cross sectional schematic view of a combination proximalanchor and plate in accordance with the present invention.

FIG. 7A is a posterior cross section as in FIGS. 1, with a plate andfixation device positioned therein.

FIG. 7B is a cross section through a proximal portion of the femur,illustrating the use of a fixation device in combination with a plate.

FIG. 7C is a cross section as in FIG. 7B, illustrating the use of afixation device of the present invention in combination with anintramedullary nail.

FIG. 8 is a cross sectional view through an angularly adjustableproximal anchor plate.

FIG. 9 is a front perspective view of the proximal anchor plate of FIG.8.

FIG. 10 is an anterior view of the distal tibia and fibula, withfixation devices across lateral and medial malleolar fractures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Although the fixation devices of the present invention will be disclosedprimarily in the context of fractures of the proximal femur, the methodsand structures disclosed herein are intended for application in any of awide variety of bones and fractures, as will be apparent to those ofskill in the art in view of the disclosure herein. For example, the bonefixation device of the present invention is applicable in a wide varietyof fractures and osteotomies in the hand, such as interphalangeal andmetacarpophalangeal arthrodesis, transverse phalangeal and metacarpalfracture fixation, spiral phalangeal and metacarpal fracture fixation,oblique phalangeal and metacarpal fracture fixation, intercondylarphalangeal and metacarpal fracture fixation, phalangeal and metacarpalosteotomy fixation as well as others known in the art. A wide variety ofphalangeal and metatarsal osteotomies and fractures of the foot may alsobe stabilized using the bone fixation device of the present invention.These include, among others, distal metaphyseal osteotomies such asthose described by Austin and Reverdin-Laird, base wedge osteotomies,oblique diaphyseal, digital arthrodesis as well as a wide variety ofothers that will be known to those of skill in the art. The bonefixation device may be used with or without plate(s) or washer(s), allof which can be either permanent, absorbable, or combinations.

Fractures of the fibular and tibial malleoli, pilon fractures and otherfractures of the bones of the leg may be fixated and stabilized with thepresent invention with or without the use of plates, both absorbable ornon-absorbing types, and with alternate embodiments of the currentinvention. Fractures and osteotomies of the mid and hind foot, tarsalarthrodesis and osteotomy, or others as are known to those with skill inthe art. One example is the fixation of the medial malleolar avulsionfragment fixation.

The fixation device of the present invention may also be used to attachtissue or structure to the bone, such as in ligament reattachment andother soft tissue attachment procedures. Plates and washers, with orwithout tissue spikes for soft tissue attachment, and other implants mayalso be attached to bone, using either resorbable or nonresorbablefixation devices depending upon the implant and procedure. The fixationdevice may also be used to attach sutures to the bone, such as in any ofa variety of tissue suspension procedures.

For example, peripheral applications for the fixation devices includeutilization of the device for fastening soft tissue such as capsule,tendon or ligament to bone. It may also be used to attach a syntheticmaterial such as marlex mesh, to bone or allograft material such astensor fascia lata, to bone. In the process of doing so, retention ofthe material to bone may be accomplished with the collar as shown, orthe pin and or collar may be modified to accept a suture or othermaterial for facilitation of this attachment.

Specific examples include attachment of the posterior tibial tendon tothe navicular bone in the Kidner operation. This application may beaccomplished using an appropriately sized implant of the presentinvention along with a washer with distally extending soft tissuespikes. Navicular-cuneiform arthrodesis may be performed utilizing thedevice and concurrent attachment of the tendon may be accomplished.Attachment of the tendon may be accomplished in the absence ofarthrodesis by altering the placement of the implant in the adjacentbone.

Ligament or capsule reattachment after rupture, avulsion or detachment,such as in the ankle, shoulder or knee can also be accomplished usingthe devices disclosed herein.

The fixation devices can also be used to aid bone fusion betweenadjacent bones, bone fragments or any of a variety of articulatingjoints, such as, for example, a first and a second adjacent vertebralbodies of the spine.

The fixation devices may be used in combination with semi tubular,one-third tubular and dynamic compression plates, both of metallic andabsorbable composition, if the collar is modified to match the openingon the plate.

The cannulated design disclosed below can be fashioned to accept anantibiotic impregnated rod for the slow adsorption of medicationlocally. This may be beneficial for prophylaxis, especially in openwounds, or when osteomyelitis is present and stabilization of fracturefragments is indicated.

A kit may be assembled for field use by military or sport medical orparamedical personnel. This kit contains an implanting tool, and avariety of implant device size and types. The kit may include additionalcomponents such as sterilization or disinfectant materials, a skinstapler, bandages, gloves, and basic tools for emergent wound andfracture treatment. Antibiotic rods may be included for woundprophylaxis during transport.

Referring to FIG. 1, there is illustrated a posterior side elevationalview of the proximal portion of a femur 10, having a two fixationdevices 12 positioned therein. The proximal end of the femur 10comprises a head 14 connected by way of a neck 16 to the long body orshaft 17 of the femur 10. As illustrated in FIG. 1, the neck 16 issmaller in diameter than the head 14. The neck 16 and head 14 also lieon an axis which, on average in humans, crosses the longitudinal axis ofthe body 17 of the femur 10 at an angle of about 126°. The risk offracture at the neck 16 is thus elevated, among other things, by theangular departure of the neck 16 from the longitudinal axis of the body17 of femur 10 and also the reduced diameter of the neck 16 with respectto the head 14.

The greater trochanter 18 extends outwardly above the junction of theneck 16 and the body 17 of the femur 10. On the medial side of thegreater trochanter 18 is the trochanteric fossa 20. This depressionaccommodates the insertion of the obturator externus muscle. The lessertrochanter 21 is located posteromedially at the junction of the neck 16and the body 17 of the femur 10. Both the greater trochanter 18 and thelesser trochanter 21 serve for the attachment of muscles. On theposterior surface of the femur 10 at about the same axial level as thelesser trochanter 21 is the gluteal tuberosity 22, for the insertion ofthe gluteus maximus muscle. Additional details of the femur are wellunderstood in the art and not discussed in further detail herein.

FIG. 1 illustrates a subcapital femoral neck fracture 24. Fractures ofthe proximal portion of the femur 10 are generally classified as capitalor subcapital femoral neck fractures, intertrochanteric fractures andsubtrochanteric fractures. All of these fractures will be deemed femoralneck fractures for the purpose of describing the present invention.

Referring to FIGS. 1-4, the fixation device 12 comprises a body 28extending between a proximal end 30 and a distal end 32. The length,diameter and construction materials of the body 28 can be varied,depending upon the intended clinical application. In embodimentsoptimized for various fractures in an adult human population, the body28 will generally be within the range of from about 6 mm to about 150 mmin length after sizing, and within the range of from about 2 mm to about12 mm in maximum diameter. The major diameter of the helical anchor,discussed below, may be within the range of from about 2.0 mm to about15 mm. In general, the appropriate dimensions of the body 28 will vary,depending upon the specific fracture. In rough terms, for a malleolarfracture, shaft diameters in the range of from about 3 mm to about 4.5mm may be used, and lengths within the range of from about 20 mm toabout 70 mm. For condylar fractures, shaft diameters within the range offrom about 3.5 mm to about 8.0 mm may be used with lengths within therange of from about 25 mm to about 70 mm. For colles fractures (distalradius and ulna), diameters within the range of from about 2.0 mm toabout 4.5 mm may be used with any of a variety of lengths within therange of from about 6 mm to about 70 mm.

In one embodiment, the body 28 comprises titanium. However, as will bedescribed in more detail below, other metals or bioabsorbable ornonabsorbable polymeric materials may be utilized, depending upon thedimensions and desired structural integrity of the finished fixationdevice 12.

The distal end 32 of the body 28 is provided with a cancellous boneanchor or distal cortical bone anchor 34. Additional details of thedistal bone anchor are described below. In general, in a femoral neckapplication, distal bone anchor 34 is adapted to be rotationallyinserted into the cancellous bone within the head 14 of the femur 10, toretain the fixation device 12 within the femoral head.

The proximal end 30 of the fixation device is provided with a proximalanchor 36. Proximal anchor 36 is axially distally moveable along thebody 28, to permit compression of the fracture 24 as will be apparentfrom FIG. 1 and the description below. As will be explained below,complementary locking structures such as threads or ratchet likestructures between the proximal anchor 36 and the body 28 resistproximal movement of the anchor 36 with respect to the body 28 undernormal use conditions. The proximal anchor 36 can be axially advancedalong the body 28 either with or without rotation, depending upon thecomplementary locking structures as will be apparent from the disclosureherein.

In the illustrated embodiment, proximal anchor 36 comprises a housing 38such as a tubular body, for coaxial movement along the body 28. Thehousing 38 is provided with one or more surface structures 40 such asradially inwardly projecting teeth or flanges, for cooperating withcomplementary surface structures 42 on the body 28. The surfacestructures 40 and complementary surface structures 42 permit distalaxial travel of the proximal anchor 36 with respect to the body 28, butresist proximal travel of the proximal anchor 36 with respect to thebody 28. Any of a variety of complementary surface structures whichpermit one way ratchet like movement may be utilized, such as aplurality of annular rings or helical threads, ramped ratchet structuresand the like for cooperating with an opposing ramped structure or pawl.

Retention structures 42 are spaced axially apart along the body 28,between a proximal limit 54 and a distal limit 56. The axial distancebetween proximal limit 54 and distal limit 56 is related to the desiredaxial working range of travel of the proximal anchor 36, and thus therange of functional sizes of the fixation device 12. In one embodimentof the fixation device 12, the retention structure 42 comprise aplurality of threads, adapted to cooperate with the retention structures40 on the proximal anchor 36, which may be a complementary plurality ofthreads. In this embodiment, the proximal anchor 36 may be distallyadvanced along the body 28 by rotation of the proximal anchor 36 withrespect to the body 28. Proximal anchor 36 may be advantageously removedfrom the body 28 by reverse rotation, such as to permit removal of thebody 28 from the patient. In this embodiment, a flange 44 is preferablyprovided with a gripping structure to permit a removal tool to rotatethe flange 44 with respect to the body 28. Any of a variety of grippingstructures may be provided, such as one or more slots, flats, bores orthe like. In one embodiment, the flange 44 is provided with a polygonal,and, in particular, a pentagonal or hexagonal circumference. See, e.g.FIG. 4A.

FIGS. 4A and 4B additionally illustrate a profile modification that canbe made on any of the embodiments discussed herein. Referring to FIG.4A, the retention structures 42 are positioned on a reduced diametersegment 31. The reduced diameter segment 31 is separated from theremainder of the body 28 by an annular shoulder 29. This constructionallows the outside diameter of the tubular housing 38 to beapproximately the same as the outside diameter of the distal portion ofbody 28. In this manner, a single diameter bore hole may be formed inthe proximal bone segment, to receive both the body 28 and tubularhousing 38 with minimal extra tolerance. Alternatively, as illustratedin FIG. 4B, the body 28 may have the same diameter throughout its axiallength with the retention structures 42 formed thereon. In thisembodiment, the outside diameter of proximal housing 38 will be largerthan the outside diameter throughout the body 28.

Thus, the present invention provides a bone fixation device which canprovide compression across a fracture throughout a range of motionfollowing the placement of the distal anchor. The distal anchor may bepositioned within the cancellous and/or distal cortical bone, and theproximal anchor may be distally advanced throughout a range to providecompression across the fracture without needing to relocate the distalanchor and without needing to initially locate the distal anchor in aprecise position with respect to the proximal side of the bone.Providing a working range throughout which tensioning of the proximalanchor is independent from setting the distal anchor allows a singledevice to be useful for a wide variety of fractures, as well aseliminates the need for accurate device measurement and accurateplacement of the distal anchor. In many applications, the working rangeis at least about 10% of the overall length of the device, and may be asmuch as 20% or 30% or more of the overall device length. In the contextof a femoral application, working ranges of up to about 10 mm may beprovided, since estimates within that range can normally be readilyaccomplished within the clinical setting. In other applications, such asa metatarsal fracture, a working range in the area of from about 1 mm toabout 2 mm may be all that is necessary. The embodiments disclosedherein can be scaled to have a greater or a lesser working range, aswill be apparent to those of skill in the art in view of the disclosureherein.

The proximal anchor 36 includes a flange 44 that seats against the outersurface of the femur or tissue adjacent the femur. The flange 44 ispreferably an annular flange, to optimize the footprint or contactsurface area between the flange 44 and the femur. Circular or polygonalshaped flanges for use in femoral head fixation will generally have adiameter of at least about 4 mm greater than the adjacent body 28 andoften within the range of from about 4 mm to about 20 mm or more greaterthan the adjacent body 28. In a modified embodiment, the flange 44 canbe curved to match the curved shape of the femur and further optimizethe footprint or contact surface area between the flange 44 and thefemur.

In the illustrated embodiment, the bone contacting surface 46 of theflange 44 resides in or approximately on a plane which is inclined withrespect to the longitudinal axis of the body 28. Any of a variety ofangular relationships between the bone contacting surface 46 of theflange 44 and the longitudinal axis of the body 28 and housing 38 may beutilized, depending upon the anticipated entrance angle of the body 28and associated entrance point surface of the femur 10. In general, thelongitudinal axis extending through the head 14 and neck 16 of the humanfemur is inclined at an angle of approximately 126° from thelongitudinal axis of the long body 17 of the femur 10. Angles betweenthe longitudinal axis of body 28 and tissue contacting surface 46 withinthe range of from about 90° to about 140° will generally be utilized,often within the range of from about 100° to about 120°, for fixed anglefixation devices. Perpendicular flanges (i.e., 90°) are illustrated inFIGS. 3A and 3B.

The clinician can be provided an array of proximal anchors 36 of varyingangular relationships between the bone contacting surface 46 and thelongitudinal axis of the body 28 and housing 38 (e.g., 90°, 100°, 110°,120°, and 130°). A single body 28 can be associated with the array suchas in a single sterile package. The clinician upon identifying theentrance angle of the body 28 and the associated entrance point surfaceorientation of the femur 10 can choose the anchor 36 from the array withthe best fit angular relationship, for use with the body 28.

In accordance with an optional feature, illustrated in FIGS. 8 and 9,the flange 44 is angularly adjustable with respect to the longitudinalaxis of the body 28. More specifically, in this embodiment, the tubularhousing 38 is a separate component from the flange 44. The housing 38and the flange 44 preferably include corresponding semi-spherical orradiused surfaces 45 a, and 45 b. The surface 45 b surrounds an aperture49 in the flange 44. This arrangement allows the housing 38 to extendthrough and pivot with respect to the flange 44. As such, the angularrelationship between the bone contacting surface 46 of the flange 44 andthe longitudinal axis of the body 28 can vary in response to theentrance angle.

As an independent feature in FIGS. 8 and 9, the flange 44 is enlargedand includes one or two or more openings 47 for receiving one or two ormore femoral shaft screws (not shown). The flange 44 may be elongatedanatomically distally parallel to the axis of the femur, so that itfunctions simultaneously as a plate, as will be discussed in connectionwith FIG. 6.

With reference back to FIGS. 3 a and 3 b, the proximal end 30 of thebody 28 is preferably additionally provided with rotational coupling 48,for allowing the body 28 to be rotationally coupled to a driving device.Any of a variety of driving devices may be utilized, such as electricdrills or hand tools which allow the clinician to manually rotate thecancellous bone anchor 34 into the head of the femur. Thus, therotational coupling 48 may have any of a variety of cross sectionalconfigurations, such as one or more flats or splines.

In one embodiment, the rotational coupling 48 comprises a proximalprojection of the body 28 having a polygonal cross section, such as ahexagonal cross section. The rotational coupling 48 is illustrated as amale component, machined or milled or attached to the proximal end 30 ofthe body 28. However, the rotational coupling may also be in the form ofa female element, such as a hexagonal or other noncircular crosssectioned lumen extending throughout a proximal portion or the entirelength of the body 28. Although illustrated as solid throughout, thebody 28 may be cannulated to accommodate installation over a placementwire as is understood in the art. The cross section of the centralcannulation can be made non circular, e.g., hexagonal, to accommodate acorresponding male tool for installation or removal of the deviceregardless of the location of the proximal break point, as will bediscussed.

The body 28 may be provided with at least one and preferably two orthree or more break points 50 spaced axially apart along the proximalportion of the body 28. Break points 50 comprise a weakened transverseplane through the body 28, which facilitate severing of the proximalportion of the body 28 following proper tensioning of the proximalanchor 36. Break point 50 may be constructed in any of a variety ofways, such as by machining or milling an annular recess into theexterior wall of the body 28, or created one or more transverseperforations through the body 28 such as by mechanical, laser, or EDMdrilling.

The body 28 may also be provided with at least one and preferably two orthree or more graduation markings axially spaced along the proximalportion of the body 28. Such graduation markings can be used to indicatehow far the body 28 has been inserted into the bone. Such graduationmarkings may include indicia indicating the distance (e.g., inmillimeters or inches) from the proximal surface of the bone to thedistal tip of the distal bone anchor 34.

In all of the embodiments illustrated herein, the distal anchor 34comprises a helical locking structure 60 for engaging cancellous and/ordistal cortical bone. In the illustrated embodiment, the lockingstructure 60 comprises a flange that is be wrapped around a central core62 or an axial lumen, as discussed below. The central core 62 or axiallumen defines a minor diameter of the helical locking structure 60. In asimilar manner, the outer edge of the helical flange 60 defines a majordiameter or outer boundary of the helical locking structure 60. Theflange extends through at least one and generally from about two toabout 50 or more full revolutions depending upon the axial length of thedistal anchor and intended application. For most femoral neck fixationdevices, the flange will generally complete from about 2 to about 20revolutions. The helical flange 60 is preferably provided with a pitchand an axial spacing to optimize the retention force within cancellousbone, to optimize compression of the fracture.

The helical flange 60 of the embodiment illustrated in FIG. 1 is shapedgenerally like a flat blade or radially extended screw thread. However,it should be appreciated that the helical flange 60 can have any of avariety of cross sectional shapes, such as rectangular, triangular orother as deemed desirable for a particular application through routineexperimentation in view of the disclosure herein. The ratio of the majordiameter to the minor diameter can be optimized with respect to thedesired retention force within the cancellous bone and giving dueconsideration to the structural integrity and strength of the distalanchor 34. Another aspect of the distal anchor 34 that can be optimizedis the shape of the major and minor diameters, which in the illustratedembodiment are generally cylindrical with a tapered distal end 32.

The distal end 32 and/or the outer edges of the helical flange 60 may beatraumatic (e.g., blunt or soft). This inhibits the tendency of thefixation device 12 to migrate anatomically proximally towards the hipjoint bearing surface after implantation (i.e., femoral head cut-out).Distal migration is also inhibited by the dimensions and presence of theproximal anchor 36, which has a larger footprint than conventionalscrews.

Referring to FIGS. 2 and 3B, a variation of the distal anchor 34 isillustrated. The distal anchor 34 comprises an elongated helical lockingstructure 60 that is spirally wrapped about an axial lumen through atleast one and preferably from about two to about 20 or more fullrevolutions. The axial lumen defines a minor diameter that is generallycylindrical. As with the previous embodiment, the elongated body 60 isprovided with a pitch and an axial spacing to optimize the retentionforce within cancellous bone, which optimizes compression of thefracture. The tip 72 of the elongated body 60 may be pointed. Althoughnot illustrated, this variation is particularly suited for a canulatedfixation device 12. That is, a design wherein a central lumen extendsthrough the body 28 and the distal anchor 34.

FIG. 5 is an axial cross sectional view through a distal anchor of thetype illustrated in FIGS. 2 and 3B. FIG. 5 also illustrates thecross-section of the helical flange which forms the spiral lockingstructure. The cross-section has a width w, and a height h. Throughroutine experimentation, the shape, the width w and height h of theelongated body can be varied to optimize the retention force withincancellous bone. When w is approximately equal to h, the cross sectioncan be circular, square or faceted. In general, w and h are within therange of from about 1 mm to about 8 mm for use in the femoral neckapplication.

With reference to FIG. 3C, another variation of the distal anchor 34 isillustrated. In this arrangement, the distal anchor 34 forms a doublehelix comprising two elongated structures 360, 362 spirally wrappedaround an axial lumen through at least one and preferably from about 2to about 20 or more full revolutions. As with the previous embodiments,the shape, the width w and height h of the elongated bodies 360, 362along with pitch and an axial spacing can be optimized through routineexperimentation to optimize the retention force within cancellous bone,which optimizes compression of the fracture. The diameter of the axiallumen can also be optimized. The tip 364 of helical flanges 360, 362 maybe tapered or pointed to permit easier insertion through self-tappingand self-drilling. The double helix design may be incorporated into anyof the designs disclosed elsewhere herein. In one embodiment for use inthe femoral neck, the elongated structures 360, 362 have a generallyrectangular cross sectional shape with a height and width within therange of about 1.0-4.0 millimeters. In such an embodiment, the majordiameter is in the range of about 4.0-15 millimeters, the minor diameteris in the range of about 2.0-8.0 millimeters, and the pitch is in therange of from about 3 to about 12 threads per inch.

With reference to FIG. 3D, yet another variation of the distal anchor 34is illustrated. In this embodiment, the anchor 34 comprises a helicalflange 370 having a generally “V” shaped cross-section. The illustratedflange 370 has sides angled at about 60-degrees, forming two loadbearing surfaces 372, 374 and a blunted outer edge 376. The proximallyfacing surface 372 carries the axial load to resist pullout. In thisembodiment of the helical flange 370, the minor diameter isapproximately equal to zero. Such an arrangement advantageously leavesmore bone in place when the distal anchor 34 is inserted into the distalbone fragment such as a portion of the femur 10. However, it should beappreciated that in a modified arrangement the minor diameter can beincreased giving due consideration to the balance between the desiredretention force within the cancellous bone and the structural integrityand strength of the distal anchor 34. The angle between the two surfaces372, 374 along with the pitch and axial spacing of the helical flange370 are selected to optimize the retention force within cancellous bone,to optimize compression of the fracture.

Still yet another variation of the distal anchor 34 is illustrated inFIG. 3E. In this variation, the distal anchor 34 comprises a helicalflange 380 having a buttress thread design. That is, the flange 380 hasa generally rectangular cross-section, and extends radially outwardlyand in some embodiments is inclined proximally to form a proximallyconcave spiral. This arrangement enhances the pullout strength of thedistal anchor 34 because the bearing surfaces 382, 384 of the flange 380lie generally perpendicular to the load direction. As with the previousarrangement, the helical flange 380 has a minor diameter that isapproximately equal to zero. However, it should be appreciated that in amodified arrangement the minor diameter can be increased minor diametercan increased giving due consideration to the balance between thedesired retention force within the cancellous bone and the structuralintegrity and strength of the distal anchor 34. As with the previousembodiments, the pitch and axial spacing can also be optimized toenhance the retention force within cancellous bone and to optimizecompression across the fracture.

Referring to FIGS. 3F and 3G, additional variations of distal anchor 34are illustrated. With initial reference to FIG. 3F, the distal anchor 34comprises at least three helical threads or flanges 390, 392, 394spirally wrapped around a generally cylindrical central core 395, whichin the illustrated arrangement also defines the wall of an axial lumen397 that can extend through the body 28. The major diameter of thedistal anchor 34 is generally cylindrical. The leading tips 396 of thehelical flanges 390, 392, 394 may be sharpened so as to aid the screw inbeing self tapping and/or self drilling. In this arrangement, thehelical flanges 390, 392, 394 can be provided with a lower pitch ascompared to the arrangement described above. Moreover, as compared tothe previous arrangements, this arrangement requires less turns toinsert the distal anchor 34 any given axial distance.

For example, in an embodiment for use in the femoral neck, the pitch ofthe helical flanges 390, 392, 394 may be within the range of from about2 to about 12 threads per inch. The distal anchor 34 therefore requiresfewer turns during insertion to achieve the same axial travel as asingle helix thread having a greater pitch. In addition, thisarrangement leaves more of the bone intact. In a modified arrangement,the distal anchor can include two or four helical flanges such asflanges 390, 392, 394. The number, pitch and axial spacing of thehelical flanges can be optimized through routine experimentation inlight of the disclosure herein. In one dual helical flange embodiment,the minor diameter is about 4.5 millimeters, the major diameter is about7.0 millimeters and the pitch is about 5.5 threads per inch.

In FIG. 3G, the distal anchor 34 comprises split triple helix distalanchor design that is similar to the arrangement described above.However, in this arrangement, one of the helical flanges is cut throughto the axial lumen 397 that is defined by the central core 395. As such,three flanges 400, 402, 403 remain wrapped around the central core 395.As compared to the previous arrangement, this arrangement leaves morebone intact. As with the previous embodiments, the pitch and axialspacing can be optimized through routine experimentation. A split doublehelix, with two flanges or threads may also be provided.

FIGS. 3H and 3I illustrate more variations of the distal anchor 34. InFIG. 3H, the distal anchor 34 comprises a generally V-shaped flange 410that is wrapped around a central core 412 that also defines a centrallumen 413, which can extend through the body 28. The major diameter ofthe V-shaped flange 410 is generally cylindrical. In contrast, the minordiameter of the central core tapers in the distal direction. As such, inthe illustrated arrangement, the central core disappears into thegenerally cylindrical central lumen 413 at a point in between theproximal and distal ends of the threads, and, in the illustratedembodiment, at approximately the longitudinal center 414 of the distalanchor 34. This arrangement strengthens the proximal portion 416 of thedistal anchor 34, where stretching and fatigue may be most likely tooccur on pullout. It is anticipated that the shape of the flange 410along with the pitch, axial spacing and the taper of the central corecan be optimized through routine experimentation given the disclosureherein.

In FIG. 3I, the distal anchor 34 also comprises a V-shaped helicalflange 420 that is wrapped around an axial lumen. In this arrangement,both the major and minor diameters taper from the proximal end 422 ofthe anchor 34 to the distal end 424. At the distal end 424, the minordiameter is approximately equal to zero. In this arrangement, the distalend 424 of tapered distal anchor 34 can provide for self tapping whilethe proximal end 422 of the anchor 34 provides for self drilling. Aswith the previous embodiments, the shape, pitch, axial spacing of thehelical flange 430 and the taper of the major and minor diameters can befurther optimized through routine experimentation. In a modifiedarrangement, the helical flange 430 can be wrapped around a central corethat tapers from the proximal end 422 to the distal end 424.

In any of the embodiments herein, an anti-rotation lock may be providedbetween the distal anchor and the proximal collar or plate, such as aspline or other interfit structure to prevent relative rotation of theproximal and distal ends of the device following implantation.

In use, the clinician first identifies a patient having a fracture to betreated, such as a femoral neck fracture, which is fixable by aninternal fixation device. The clinician accesses the proximal femur,reduces the fracture if necessary and selects a bone drill and drills ahole 80 in accordance with conventional techniques. In the example of afemoral neck fracture, three holes and fixation devices will often beused as has been discussed. Preferably, the hole 80 has a diameterwithin the range from about 3 mm to about 8 mm. This diameter may beslightly larger than the diameter of the distal anchor 34. The hole 80preferably extends up to or slightly beyond the fracture 24.

A fixation device 12 having an axial length and outside diametersuitable for the hole 80 is selected. The distal end 32 of the fixationdevice 12 is advanced distally into the hole 80 until the distal anchor34 reaches the distal end of the hole 80. The proximal anchor 36 may becarried by the fixation device 12 prior to advancing the body 28 intothe hole 80, or may be attached following placement of the body 28within the hole 80. Once the body 28 is in place, the clinician may useany of a variety of driving devices, such as electric drills or handtools to rotate the cancellous bone anchor 34 into the head of thefemur.

While proximal traction is applied to the proximal end 30 of body 28,such as by conventional hemostats, pliers or a calibrated loadingdevice, the proximal anchor 36 is advanced distally until the anchor 36fits snugly against the outer surface of the femur or tissue adjacentthe femur. Appropriate compression of the fixation device 12 across thefracture is accomplished by tactile feedback or through the use of acalibration device for applying a predetermined load on the implantationdevice. One advantage of the structure of the present invention is theability to adjust compression independently of the setting of the distalanchor 34.

Following appropriate tensioning of the proximal anchor 36, the proximalextension 30 of the body 28 is preferably cut off, snapped off,unscrewed or otherwise removed. Body 28 may be cut using conventionalsaws, cutters or bone forceps which are routinely available in theclinical setting. Alternatively, the fixation device can be selectedsuch that it is sized to length upon tensioning, so that no proximalprojection remains.

Following removal of the proximal end 30 of body 28, the access site maybe closed and dressed in accordance with conventional wound closuretechniques.

With reference to FIG. 2, in one arrangement, the proximal anchor 36 caninclude one or more barbs 41 extending radially outwardly from thetubular housing 28. The barbs 41 may be radially symmetricallydistributed about the longitudinal axis of the tubular housing 38. Eachbarb 41 is provided with a transverse engagement surface 43, foranchoring the proximal anchor 36 in the bone. The transverse engagementsurface 43 may lie on a plane which is transverse to the longitudinalaxis of the tubular housing 38 or may be inclined with respect to thelongitudinal axis of the tubular housing 38. In either arrangement, thetransverse engagement surface 43 generally faces the bone contactingsurface 46 of the flange 44. As such, the transverse engagement surface43 inhibits proximal movement of the proximal anchor 36 with respect tothe bone.

The barbs 41 allow the bone fixation device to capture “secondarycompression” of the fracture. As explained above, the bone fixationdevice can be used to provide an initial compression across the fracturewhen the proximal anchor 36 is appropriately tensioned. However, as thepatient applies weight or stress to the bone post procedure, thefracture typically undergoes secondary compression, which furthercompresses the fracture. During such secondary compression, the barbs 41prevent proximal movement of the proximal anchor 36 with respect to thebone. The ratchet-type structures 40, 42 of the proximal anchor 36 andthe body 28 allow the proximal anchor 36 to move distally along the body28. Thus, any slack caused by the secondary compression is taken up bythe proximal anchor 36 as the retention structures 40, 42 preventproximal movement of the proximal anchor 36 with respect to the body 29.This device is therefore self tightening after it has been implanted inthe patient.

Preferably, the clinician will have access to an array of fixationdevices 12, having, for example, different diameters, axial lengths andangular relationships. These may be packaged one per package in sterileenvelopes or peelable pouches, or in dispensing cartridges which mayeach hold a plurality of devices 12. Upon encountering a fracture forwhich the use of a fixation device is deemed appropriate, the clinicianwill assess the dimensions and load requirements, and select a fixationdevice from the array which meets the desired specifications.

In some types of fractures such as a femoral neck fracture, a clinicianmay want to introduce two or three or more fixation devices 12 into thefemoral head 14 to secure the fracture 24. This may be desirable if theclinician determines that, based upon the nature of the fracture 24,there is a possibility that the head 14 of the femur 10 could rotateabout a single fixation device 12. Even minor rotation can inhibit thehealing of the fracture. Significant rotation can result in failure ofthe fixation device or necrosis of the femoral head. Two fixationdevices 12 may also be desirable where the direction of the fracture isgenerally parallel to the axis of implantation as is understood in theart.

Referring to FIG. 6, there is disclosed a variation of the proximalanchor 36 in which the proximal anchor 36 is integrally formed with orattached to a plate. The fixation device 12 in FIG. 6 may otherwise beidentical to the embodiments previously discussed. The proximal anchor90 comprises an elongated flange 92, which extends from the housing 93longitudinally down (anatomically caudad or distally) the body 17 of thefemur 10. The elongated flange 92 preferably includes one or moreopenings 94 for receiving one or more femoral shaft screws 96. Theflange 92 may or may not extend above (anatomically proximal to) thehousing 93. Elimination of a proximal flange may more easily permitrotational removal of the proximal anchor 36 from the body 28 by reverserotation in an inclined flange embodiment.

Referring to FIG. 6A, there is illustrated a cross sectional schematicview of an integral proximal anchor 36 and proximal plate. Thedimensions and orientation of the proximal anchor 36 may be variedwidely, depending upon the intended application. For example, alongitudinal axis of the housing 93 may be inclined or perpendicularwith respect to the plane of flange 92. The flange 92 may have any of avariety of dimensions and profiles, depending upon the intendedapplication. Lengths of the plate 92 in the vertical direction asillustrated on FIG. 6A, for use in femoral neck fixation fractures, mayrange from at least about 0.5 inches to about 10 inches or more. Theplate 92 may be planar as illustrated, particularly in small plateembodiments, or may be curved or contoured to improve seating of theplate 92 against the adjacent bone. Plate 92 may be provided with one ormore apertures for receiving bone screws or other fixation devices asillustrated in FIGS. 6 and 7A.

Referring to FIG. 7A, the fixation device 12 is schematicallyillustrated in combination with a conventional plate 100. The fixationdevice 12 in FIG. 7A may be identical to the embodiments describedelsewhere herein. The fixation device 12 is used with an elongated sidesupport or plate 100, which extends longitudinally above and below thehole 80. The elongated side plate 100 includes an opening 102 thatpreferably has a diameter that is slightly larger than the diameter ofthe housing 38. The elongated side plate 100 preferably also includesone or more openings 104 for receiving one or more femoral shaft screws106. Advantageously, the elongated side plate 100 spreads the forcesexerted by the flange 44 across a larger area of the femur 17, andaffects the distribution of load. In an alternate embodiment, theelongated side plate can 100 include one or more openings above thehousing 38 for receiving trochanteric anchor screws (not shown).

A contoured side plate 100 is illustrated in FIG. 7B. The proximalanchor 36 is also formed with a tapered (e.g. conical or concaveoutwardly) bone or plate contacting surface on flange 44.

The fixation device 12 of the present invention may also be used incombination with intramedullary nails or rods 101 as schematicallyillustrated in FIG. 7C, as will be understood by those of skill in theart.

The fixation device 12 of the present invention may be used in any of awide variety of anatomical settings beside the proximal femur, as hasbeen discussed. For example, lateral and medial malleolar fractures canbe readily fixed using the device of the present invention. Referring toFIG. 10, there is illustrated an anterior view of the distal fibula 120and tibia 122. The fibula 120 terminates distally in the lateralmalleolus 124, and the tibia 122 terminates distally in the medialmalleolus 126.

A fixation device 12 in accordance with the present invention isillustrated as extending through the lateral malleolus 124 across thelateral malleolar fracture 128 and into the fibula 120. Fixation device12 includes a distal anchor 34 for fixation within the fibula 120, anelongate body 28 and a proximal anchor 36 as has been discussed.

FIG. 10 also illustrates a fixation device 12 extending through themedial malleolus 126, across a medial malleolar fracture 130, and intothe tibia 122. Although FIG. 10 illustrates fixation of both a lateralmalleolar fracture 128 and medial malleolar fracture 130, eitherfracture can occur without the other as is well understood in the art.Installation of the fixation devices across malleolar fractures isaccomplished utilizing the same basic steps discussed above inconnection with the fixation of femoral neck fractures.

The fixation devices of the present invention may be made from eitherconventional bioabsorbable materials or conventional non-absorbablematerials, combinations thereof and equivalents thereof. In addition,natural materials such as allografts may be used. Examples of absorbablematerials include homopolymers and copolymers of lactide, glycolide,trimethylene carbonate, caprolactone, and p-dioxanone and blendsthereof. The following two blends may be useful:

(1) the blend of poly(p-dioxanone) and a lactide/glycolide copolymer, asdisclosed in U.S. Pat. No. 4,646,741 which is incorporated by reference.

(2) the glycolide-rich blend of two or more polymers, one polymer beinga high lactide content polymer, and the other being a high glycolidecontent disclosed in U.S. Pat. No. 4,889,119 which is incorporated byreference.

Additional bioabsorbable materials are disclosed in copendingapplication Ser. No. 09/558,057 filed Apr. 26, 2000, the disclosure ofwhich is incorporated in its entirety herein by reference.

The fixation devices may also be made from conventional non-absorbable,biocompatible materials including stainless steel, titanium, alloysthereof, polymers, composites and the like and equivalents thereof. Inone embodiment, the distal anchor comprises a metal helix, while thebody and the proximal anchor comprise a bioabsorbable material.Alternatively, the distal anchor comprises a bioabsorbable material, andthe body and proximal anchor comprise either a bioabsorbable material ora non-absorbable material. As a further alternative, each of the distalanchor and the body comprise a non-absorbable material, connected by anabsorbable link. This may be accomplished by providing a concentric fitbetween the distal anchor and the body, with a transverse absorbable pinextending therethrough. This embodiment will enable removal of the bodyfollowing dissipation of the pin, while leaving the distal anchor withinthe bone.

The components of the invention (or a polymeric coating layer on part orall of the anchor surface), may contain one or more bioactivesubstances, such as antibiotics, chemotherapeutic substances, angiogenicgrowth factors, substances for accelerating the healing of the wound,growth hormones, antithrombogenic agents, bone growth accelerators oragents, and the like. Such bioactive implants may be desirable becausethey contribute to the healing of the injury in addition to providingmechanical support.

In addition, the components may be provided with any of a variety ofstructural modifications to accomplish various objectives, such asosteoincorporation, or more rapid or uniform absorption into the body.For example, osteoincorporation may be enhanced by providing amicropitted or otherwise textured surface on the components.Alternatively, capillary pathways may be provided throughout the bodyand collar, such as by manufacturing the anchor and body from an opencell foam material, which produces tortuous pathways through the device.This construction increases the surface area of the device which isexposed to body fluids, thereby generally increasing the absorption ratein a bioabsorbable construction. Capillary pathways may alternatively beprovided by laser drilling or other technique, which will be understoodby those of skill in the art in view of the disclosure herein. Ingeneral, the extent to which the anchor can be permeated by capillarypathways or open cell foam passageways may be determined by balancingthe desired structural integrity of the device with the desiredreabsorption time, taking into account the particular strength andabsorption characteristics of the desired polymer.

One open cell bioabsorbable material is described in U.S. Pat. No.6,005,161 as a poly(hydroxy) acid in the form of an interconnecting,open-cell meshwork which duplicates the architecture of human cancellousbone from the iliac crest and possesses physical property (strength)values in excess of those demonstrated by human (mammalian) iliac crestcancellous bone. The gross structure is said to maintain physicalproperty values at least equal to those of human, iliac crest,cancellous bone for a minimum of 90 days following implantation. Thedisclosure of U.S. Pat. No. 6,005,161 is incorporated by reference inits entirety herein.

The components of the present invention may be sterilized by any of thewell known sterilization techniques, depending on the type of material.Suitable sterilization techniques include heat sterilization, radiationsterilization, such as cobalt 60 irradiation or electron beams, ethyleneoxide sterilization, and the like.

The specific dimensions of any of the bone fixation devices of thepresent invention can be readily varied depending upon the intendedapplication, as will be apparent to those of skill in the art in view ofthe disclosure herein. Moreover, although the present invention has beendescribed in terms of certain preferred embodiments, other embodimentsof the invention including variations in dimensions, configuration andmaterials will be apparent to those of skill in the art in view of thedisclosure herein. In addition, all features discussed in connectionwith any one embodiment herein can be readily adapted for use in otherembodiments herein. The use of different terms or reference numerals forsimilar features in different embodiments does not imply differencesother than those which may be expressly set forth. Accordingly, thepresent invention is intended to be described solely by reference to theappended claims, and not limited to the preferred embodiments disclosedherein.

1. A femoral neck fracture fixation device, comprising: an elongatebody, having a proximal end and a distal end; a helical anchor on thedistal end, the helical anchor being wrapped about a central core whichdefines a minor diameter of the helical anchor, an outer edge of thehelical anchor defining an outer boundary; a first retention structureon the body, proximal to the anchor; and a proximal anchor, moveablycarried by the body, wherein the proximal anchor is movable in thedistal direction with respect to the body and the retention structureresists proximal movement of the proximal anchor with respect to thebody and; wherein the central core includes an axial lumen, the axiallumen extending from the proximal end of the body to the distal end ofthe body to accommodate placement of the elongate body over a placementwire.
 2. A femoral neck fracture fixation device as in claim 1, whereinthe outer boundary and the minor diameter are generally cylindrical. 3.A femoral neck fracture fixation device as in claim 2, wherein the minordiameter tapers distally.
 4. A femoral neck fracture fixation device asin claim 2, wherein at a distal end of the distal anchor the outerboundary tapers.
 5. A femoral neck fracture fixation device as in claim2, wherein the helical flange is a generally flat blade.
 6. A femoralneck fracture fixation device as in claim 1, wherein the helical anchorcomprises at least a first flange, and a second flange.
 7. A femoralneck fracture fixation device as in claim 6, wherein the outer boundaryand the minor diameter are generally cylindrical.
 8. A femoral neckfracture fixation device as in claim 1, wherein the helical anchorcomprises at least a first flange, a second flange, and a third flange.9. A femoral neck fracture fixation device as in claim 8, wherein theouter boundary and the minor diameter are generally cylindrical.
 10. Afemoral neck fracture fixation device as in claim 8, wherein at leastthe third flange is removed so as to expose the axial lumen.
 11. Afemoral neck fracture fixation device as in claim 10, wherein the outerboundary and the minor diameter are generally cylindrical.
 12. A femoralneck fracture fixation device as in claim 1, wherein the central coretapers in a distal direction so as to expose the axial lumen.
 13. Afemoral neck fracture fixation device as in claim 12, wherein the axiallumen is exposed at approximately a longitudinal center of the distalanchor.
 14. A femoral neck fracture fixation device as in claim 1,wherein the minor diameter tapers in a distal direction.
 15. A femoralneck fracture fixation device as in claim 14, wherein at a distal end ofthe helical anchor the minor diameter is approximately equal to zero.16. A femoral neck fracture fixation device as in claim 14, wherein theouter boundary also tapers in a distal direction.
 17. A bone fixationdevice, comprising: an elongate body having a proximal end and a distalend; a cancellous bone anchor on the distal end; the cancellous boneanchor comprising a helical flange wrapped about a central core thatdefines an axial lumen, an outer edge of the helical flange defining anouter boundary and the central core defining a minor diameter; aproximal anchor axially movably carried on the body; and complimentarysurface structures in between the body and the proximal anchor thatpermit advancing the proximal anchor in the distal direction to tightenthe fixation device but that resist axial proximal movement of theproximal anchor; wherein the axial lumen extends from the proximal endof the body to the distal end of the body.
 18. A fixation device as inclaim 17, wherein the outer boundary and the minor diameter aregenerally cylindrical.
 19. A femoral neck fracture fixation device as inclaim 18, wherein at a distal end of the bone anchor the minor diametertapers.
 20. A femoral neck fracture fixation device as in claim 18,wherein at a distal end of the bone anchor the outer boundary tapers.21. A femoral neck fracture fixation device as in claim 18, wherein thehelical flange is a generally flat blade.
 22. A fixation device as inclaim 17, wherein the helical flange comprises at least a first flangeand a second flange.
 23. A fixation device as in claim 22, wherein theouter boundary and the minor diameter are generally cylindrical.
 24. Afixation device as in claim 17, wherein the helical flange comprises atleast a first flange, a second flange, and a third flange.
 25. Afracture fixation device as in claim 24, wherein the outer boundary andthe minor diameter are generally cylindrical.
 26. A femoral neckfracture fixation device as in claim 24, wherein at least the thirdflange is removed so as to expose the axial lumen.
 27. A femoral neckfracture fixation device as in claim 26, wherein the outer boundary andthe minor diameter are generally cylindrical.